Self-assembly of structured CeCO3OH and its decomposition in H2 for a novel tactic to obtain CeO2-x with excellent photocatalytic property

Abstract In this work, various new-observed structured CeCO3OH were synthesized by a self-assembly hydrothermal method, and a novel tactic to produce CeO2-x with excellent photocatalytic activity by decomposing CeCO3OH in H2 was proposed and identified. By controlling the synthetic conditions, almond-like, subglobose shape and hollow-sphere of CeCO3OH, 3D-broom-like of Ce2O3·2CO2·nH2O (n=(1-2)), and sheet-like of Ce2(CO3)3·6H2O were synthesized. The crystal growth and formation of the cerium carbonate compounds were carefully studied using XRD, SEM and TEM. TG, thermodynamic calculation and in-situ XRD were employed to reveal the decomposition behavior of almond-like CeCO3OH in air, Ar and H2. The results show that the decomposition temperatures of CeCO3OH in Ar and H2 are higher than that of in air, and suggest that Ce2O3 has a low thermodynamic stability during the decomposition of CeCO3OH in Ar and H2, and Ce3+ will be mostly oxidized by H2O firstly and then by both of H2O and CO2. The ceria samples obtained by decomposing from CeCO3OH in different atmosphere maintain indistinguishable shape and particle size. The XPS, Raman spectra and ESR results indicate that the one obtained in H2 has the richest surface oxygen vacancies (OVs), narrowest band gap of 3.12 eV, lowest intensity in PL spectra and a significantly enhanced photodegradation ratio of methylene blue. The MB photodegradation ratio after 120 min reaction with the catalysts of CeO2-Air, CeO2-Ar and CeO2-H2 is 43.14, 54.43 and 73.41%, with a calculated reaction rate constant of 0.00539，0.00652 and 0.01097 min-1, respectively. The offered novel tactic of decomposing CeCO3OH in H2 is an efficient and facile technique for active CeO2-x production.